Biodegradable formed article

ABSTRACT

Compositions of the invention include a hydroxy-functional polyester and a natural polymer. Articles can be made from such a composition so as to have sufficiently strong tensile strengths as to form disposable utensils or to have sufficient stretchability so as to form thin wrap films. However, the compositions are more environmentally friendly than commodity plastics such as polyethylene or polystyrene. Granular starches derived from a grain, a root, a legume, or mixtures thereof, are particularly preferred as the natural polymers for inclusion in the compositions.

This is a division of application Ser. No. 08/804,376, filed Feb. 21,1997, and now U.S. Pat. No. 5,852,078 which claims priority fromprovisional application Ser. No. 60/013,526, filed Feb. 28, 1996.

FIELD OF THE INVENTION

The present invention generally relates to compositions useful forforming articles by means such as thermoplastic processing (e.g.,molding, extrusion and casting), and more particularly relates tohydroxy-functional polyester containing compositions. Articles with goodmechanical properties, such as tensile strength and/or tensileelongation, can be made with such polyesters in combination with naturalpolymers. Such articles are biodegradable and have a reduced cost ofmanufacture due to the inclusion of a low cost natural polymer, such asstarch.

This invention was made with government support under Grant Agreementnumber 59-3K95-3-126 awarded by the United States Department ofAgriculture, Agricultural Research Services. The government has certainrights in this invention.

BACKGROUND OF THE INVENTION

Starches and modified starches have been the focus of considerableresearch interest in attempts to use these as fillers in order todecrease polymer costs and to use polymers that are biodegradable. Asseveral recent examples, U.S. Pat. No. 5,384,187, issued Jan. 24, 1995,inventors Uemura et al., U.S. Pat. No. 5,391,423, issued Feb. 21, 1995,inventors Wnuk et al., and U.S. Pat. No. 5,412,005, issued May 2, 1995,inventors Bastioli et al., all represent domestic and foreign basedattempts to achieve biodegradable polymer compositions in which naturalpolymers such as starches have been added to synthetic polymers.Unfortunately, while the inclusion of starches can reduce costs, themechanical properties of the synthetic polymer can be so adverselyaffected by inclusion of starch as to vitiate the cost advantages.

Among examples of physical strength loss when starch is blended withvarious synthetic polymers are those described in several recentarticles. Thus, for example, Koenig and Huang, TMSE, 67, pp. 290-291(1992) used three different types of synthetic polymers in combinationwith starch and starch derivatives and reported their properties. Whenpolycaprolactone ("PCL") was filled with 25 wt. % starch or a starchderivative the yield strength and the tensile strength were reduced byhalf.

Ramsay et al., Applied and Environmental Microbiology, 59, pp. 1242-1246(1993) studied poly-β-hydroxyalkanoates with starch. The biodegradablepolymer [P(HB-co-HV)] was said to hold biodegradable promise, but thepolymer is significantly higher in price than a commodity plastic suchas polyethylene or polystyrene. The inclusion of 25 wt. % granularstarch was reported to result in a composition with a tensile strengthof about 60% the original (16 MPa by contrast to 27 MPa). The authorsacknowledged that the use of unmodified granular starch as a particulatefiller in the [P(HB-co-HV)] polymer reduced the tensile strength and didnot offer any appreciable reinforcement in the mechanical rigidity,presumably due to poor adhesion of the polymer granule interface. Theauthors concluded it would be necessary to develop formulations withimproved adhesion.

Accordingly, attempts continue to find synthetic polymer basedcompositions that can be formed into articles, such as for exampledisposable plastic utensils or stretchable thin films for food packagingpurposes, that are reasonably competitive in price with commodityplastics such as polyethylene or polystyrene, but which are moreenvironmentally friendly.

SUMMARY OF THE INVENTION

The present invention has several embodiments that solve the problemsdiscussed above.

In one aspect of the present invention, a formed article comprises acontinuous synthetic polymer phase and a discontinuous natural polymerphase. The synthetic polymer phase includes a hydroxy-functionalpolyester that is surprisingly compatible with the natural polymerphase.

Articles of this embodiment can be formulated so as to have a tensilestrength above about 20 MPa (sufficiently strong for example, so as toform disposable utensils) or to have a tensile elongation above about200% (sufficient stretchability, for example, so as to form thinwrapping films). With one particularly preferred embodiment, acomposition is provided with 45 wt. % starch granules (derived fromcorn) having an elongation of about 500%. In another particularlypreferred embodiment, a composition is provided with 60 wt. % starchgranules (derived from corn) having a tensile strength of about 22 MPa.

The hydroxy-functional polyesters with which inventive compositions andarticles may be formed by inclusion of natural polymer granules show aremarkable compatibility with natural polymers. This is illustrated bytests showing that inclusion of small amounts of granular starch intoseveral hydroxy-functional polyesters actually increases the tensilestrength of the hydroxy-functional polyester. Another example of theremarkable compatibility of the hydroxy-functional polyesters andgranular starch is shown in instances where inclusion of plasticizeractually leads to moderately improved tensile strength although presenceof plasticizer in other polymer compositions typically softens suchcompositions.

Compositions of the invention are useful for formed articles,particularly by thermoforming techniques such as molding, extrusion andcasting, and preferably comprise a hydroxy-functional polyester, such asa poly(hydroxyester) or a poly(hydroxyester ether), admixed with starchor modified starch granules derived from a grain, a root, a legume, atuber, or mixtures thereof. By "modified" is meant that the starch canbe derivatized or modified by typical processes known in the art (e.g.esterification, etherification, oxidation, acid hydrolysis,cross-linking and enzyme conversion). Thus, for example, a modifiedstarch may be a starch ester, a starch ether, or a crosslinked starch.Conventional modifications of starch are described in publications suchas Starch: Chemistry and Technology, 2d edition, editor Whistler et al.,and Starch Derivatives: Production and Uses, Rutenberg et al., AcademicPress, Inc. 1984.

The granules preferably have less than about 15 wt. % water andpreferably have a particle size of less than about 50 μm.

In addition to the two essential components of hydroxy-functionalpolyester and natural polymer, compositions of the invention canoptionally include various additional materials, such as for exampleplasticizers, and filler materials, such as for example cellulose,vegetable fibers, calcium carbonate, talc, etc.

Other advantages and aspects of the present invention will becomeapparent upon reading the specification and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph of one inventive embodiment ata magnification of 1000; and

FIG. 2 is another scanning electron microgram of another inventiveembodiment, but again at a magnification of 1000, and was made followingan elongation test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Broadly, the present invention comprises a composition consistingessentially of two essential components: the first component is anhydroxy-functional polyester, and the second component is a naturalpolymer. The natural polymer is preferably in the form of granulesderived from starch or a derivatized (modified) starch, but can also begranules of other natural polymers (e.g. guar gum, cellulose and thelike). Granules should have a particle size of less than about 100 μm,and preferably have a particle size of up to 50 μm and a water contentof less than about 15 wt. %, more preferably less than about 10 or 11wt. %.

These two essential components are admixed in varying amounts. Thenatural polymer may be present in a trace amount or in greater amountsup to a weight ratio with respect to the hydroxy-functional polyester ofabout 8:1, more preferably up to about 6:1. Each of the componentssuitable for preparing compositions of the invention will now be morefully described.

Suitable Hydroxy-Functional Polyesters

Useful hydroxy-functional polyesters for this invention may be preparedfrom base-catalyzed nucleophilic addition of suitable acids to epoxies,which reaction generates both an ester linkage and a pendent hydroxylgroup. Transesterification and cross linking reactions are eliminatedthrough use of quaternary ammonium halide salts as initiators for thereaction of diacids with diglycidyl ethers, providing convenientpreparation of high molecular weight, thermoplastic, hydroxy-functionalpolyesters in ether solvents at temperatures from 80° C.-160° C. Thepreparation and structures for such hydroxy-functional polyesterssuitable in practicing this invention may be as described by U.S. Pat.No. 5,171,820, inventors Mang and White, issued Dec. 15, 1992, which ishereby incorporated in its entirety by reference. Data provided by theDow Chemical Company (manufacturer of hydroxy-functional polyesters suchas described by U.S. Pat. No. 5,171,820) indicates the biodegradablenature of these polymers through the ability of various soil bacteria(such as Pseudomonas putida) to use the synthetic polymers as asubstrate for cell culture growth.

Representative structures for suitable hydroxy-functional polyesters inpracticing this invention are preferably represented by Formula A (wheren provides a sufficient molecular weight, such as for example a m.w. ofabout 50,000-100,000). Higher molecular weights are preferred due tohigher strength. ##STR1## In Formula A each of R¹ and R² is individuallya divalent organic moiety which is predominately hydrocarbon, each R³ isindividually hydrogen or lower alkyl, y is a fraction from 0 to 0.5 andx is a fraction from about 0.05 to about 0.4. Typically Y is hydrogen orglycidyl and Y' is glycidyl arylene ether, glycidyl alkyene ester,glycidyl alkylene ether or glycidyl arylene ester.

Thus, suitable polyesters have repeating units represented by Formula B(where each of R¹, R², R³, x, and y are as defined above). ##STR2##

Particularly preferred such polyesters are prepared from diglycidylesters of an aliphatic diacid such as adipic due to the readyavailability and reasonable price for adipic acid as a source ofreactant. Other particularly preferred polyesters may be prepared fromdihydric phenols, such as hydroquinone.

Four particularly preferred hydroxy-functional polyesters, usedextensively to illustrate (but not to limit) the present invention, aresometimes hereinafter designated "BIS CHD," "BIS Adipic," "HQ DDCA" and"BIS DDCA." Repeating unit structures for these four illustrativehydroxy-functional polyesters are illustrated by Formulas C-F andseveral of their properties of interest for the invention are summarizedin Table A. ##STR3##

In the Formulas C-F, "n" preferably is as earlier described.

                  TABLE A                                                         ______________________________________                                        Hydroxy-Functional   Tensile                                                    Polyester Components Tg(°C.) Strength (MPa) % Elongation             ______________________________________                                        BIS CHD     66       60-61       172                                            BIS Adipic 45 12 157                                                          HQ DDCA 10 14 612                                                             BIS DDCA 20 1.2 487                                                         ______________________________________                                    

With reference to the data of Table A, one sees that two of thehydroxy-functional polyesters used to illustrate this invention have aquite high percentage elongation property (HQ DDCA and BIS DDCA). Thus,one would tend to choose one of these (or another with a relatively highpercentage elongation property) when one wished to formulate anembodiment of the invention that had high percent elongation. Similarly,if one wished to formulate an inventive embodiment with outstandingtensile strength, a hydroxy-functional polyester such as BIS CHD couldbe chosen; however, due to the remarkable compatibility of naturalpolymers with the hydroxy-functional polyesters, even a polyester with arelatively modest tensile strength, such as BIS adipic, can beformulated to have substantially improved tensile strength. This will bedemonstrated hereinafter by Table 3 of Example 4.

Natural Polymers

Among the natural polymers suitable and preferred for practicing thisinvention is starch. Starch is a low-cost and abundant natural polymercomposed of amylose and amylopectin. Amylose is essentially a linearpolymer having a molecular weight in the range of 100,000-500,000,whereas amylopectin is a highly branched polymer having a molecularweight of up to several million. Unmodified, natural starches areobtained in granular form and may be derived from cereals or grains(such as corn, wheat, rice and sorghum), roots (such as cassava),legumes (such as peas), and tubers such as potato and canna. Such starchgranules typically have a particle size less than about 50 μm, which isthe preferred particle size. While less preferred, flours whose contentsare predominately starch, and which may also contain protein, oil andfiber, are operative in the invention. Where such other natural polymersare used, they should be processed so as to be in granular form andpreferably will have a relatively uniform particle size of about 50 μmor less. Starches derived from potato and canna are also less preferredfor use in this invention due to their relatively large particle size ofabout 40 μm to about 100 μm.

Starch granules for use in this invention will normally have a watercontent of less than about 15 wt. %, more preferably less than about10-11 wt. %. As will be exemplified, granules may be pre-dried to lessthan about 1% moisture before compounding. Although preferred,pre-drying is not believed necessary.

Derivatized (modified) starches are also suitable for use in thisinvention. By "derivatized starches" is meant to include starches whichhave been chemically treated so as to form starch esters, starch ethers,and crosslinked starches. By "modified" is meant that the starch can bederivatized or modified by typical processes known in the art (e.g.esterification, etherification, oxidation, acid hydrolysis,cross-linking and enzyme conversion). Typically, modified starchesinclude esters, such as the acetate ester of dicarboxylicacids/anhydrides. Particularly useful are the alkenyl-succinic acids,and hydrides, ethers (such as the hydroxyethyl and hydroxypropylstarches), starches oxidized with hypochlorite, starches reacted withcross-linking agents such as phosphorus oxychloride, epichlorhydrin,hydrophobic cationic epoxides, and phosphate derivatives prepared byreaction with sodium or potassium orthophosphate or tripolyphosphate andcombinations thereof. These and other conventional modifications ofstarch are described in publications such as Starch: Chemistry andTechnology, 2d edition, editor Whistler et al., and Starch Derivatives:Production and Uses, Rutenberg et al., Academic Press, Inc. 1984.

For example, starch esters may be prepared using a wide variety ofanhydrides, organic acids, acid chlorides, or other esterificationreagents. Examples of anhydrides are acetic, propionic, butyric, and soforth. Further, the degree of esterification can vary as desired, suchas from one to three per glucosidic unit of the starch, or asappropriate given the number of hydroxyl groups in the monomeric unit ofthe natural polymer, if selected to be other than starch. Similar ordifferent esterified natural polymers, with varying degrees ofesterification, can be blended together for practicing the invention.Although esterified starches are stable to attack by amylases, in theenvironment the esterified starches are attached by microorganismssecreting esterases which hydrolyze the ester linkage.

Starch esters tend to be hydrophobic in contrast to starch raw materials(that is, derived by usual techniques from natural sources such ascorn). Thus, depending upon the particular application, one may preferto choose an hydrophobic starch ester rather than a hydrophilic starchin formulating compositions of the invention.

Starches are preferred for use as the natural polymers, particularly dueto ready availability and low cost, but other suitable natural polymers(in or prepared to be in granular form of a suitable particle size) arehydroxyl containing polymers such as cellulose, hemicellulose, chitin,guar gum, locust bean gum, pectin, xanthan, algin, agar, and dextran.Some of these can play the role of filler, also. Excellent results havebeen obtained with both granulated guar gum and cellulose powder, aswill be exemplified hereinafter.

Optional Components

A plasticizer can be added to inventive compositions to achieve greatermaterial processability and product flexibility, although plasticizerstypically soften the compositions in which they are included. This isnot always true, however, of compositions of the invention, as will bediscussed hereinafter. Molded articles and films prepared from blendsincluding plasticizers preferably use plasticizers that arebiodegradable. Examples of biodegradable plasticizers include variousesters, such as phthalate esters, and various other biodegradable estersknown in the chemical arts.

Inorganic and organic fillers can be added, such as talc, calciumcarbonate, diatomaceous earth, and so forth. Biodegradable organicfillers, such as cellulose and other fibers and the like are well known.

Compositions of the invention, as earlier noted, can be processed byvarious methods such as extrusion, injection molding, and film formingmethods. For example, extrusion casting can give translucent, flexiblefilms.

EXPERIMENTAL

Aspects of the invention will now be illustrated, without intending anylimitation, by the following examples.

EXAMPLE 1

Inventive embodiments were prepared from premixed batches of starch orderivatized starch and polyester and optionally containing plasticizeror other additives. The starches were pre-dried to less than 1% moisturebefore compounding. Compounding was then accomplished on a BrabenderPL2000 torque rheometer using a mixing screw with a fluted dispersivemixing section and a notched distributive section. Strands from the diewere air cooled and pelletized.

The compounded pellets were then injection molded into tensile bars(ASTM D638 Type V) either with a Cincinnati Millicron Model ACT-75B or aRabit Hy-4 ram-type machine with a single cavity mold. For somecompositions tensile bars were stamped from compression molded blanksformed in a Carver Press. Tensile bars were conditioned at 50% RH and23° C. for one day before testing in order to provide equivalentconditions in comparing one run to another. Selected compositions werealso tested after immersion in water for one day.

Tensile tests were performed on an Instron Model 4201 testing system.

As illustrated by the Tables 1-5 and Table 6 data, inventive compositionmay be made as formed articles. Compositions of the invention aresuitable for thermoplastic processing, such as molding, extrusion andcasting, in applications where solid articles are desired as well aswhere thin, stretchable films are desired. A limitation is placed on thestarch content (e.g. above about 70 wt. % or 80 wt. %) forprocessability.

EXAMPLE 2

Embodiments of the invention were prepared as described by Example 1.Four were selected for having a tensile strength above about 20 MPa, asis set out by the data of Table 1. The natural polymer used for all fourcompositions was corn derived starch granules.

                  TABLE 1                                                         ______________________________________                                        Inventive                                                                              Wt. %    Wt. %            Tensile                                      Composition Starch Polymer.sup.a Other Strength (MPa)                       ______________________________________                                        1        15       85        --     66.3                                         2 30 70 -- 39.0                                                               3 45 55 -- 22.0                                                               4 60 40 -- 23.3                                                             ______________________________________                                         .sup.a The hydroxyfunctional polyester was BIS CHD.                      

The inventive composition 1 is remarkable in its tensile strengthproperty when one considers that the tensile strength of 100% BIS CHDpolymer is 60-61 MPa. This means the inventive composition with 15 wt. %starch has a tensile strength that is increased with respect to thepolyester itself. This is another illustration of the remarkablecompatibility between natural polymers, such as the granular starchcomponent, and the hydroxy-functional polyester for compositions of theinvention.

Returning to the data of Table 1, although inventive compositions 3 and4 had only about 1/3 the tensile strength in comparison to a compositionwith all polyester, nevertheless even the highly starch filledcomposition had a tensile strength adequate for forming a number ofuseful articles, such as for example disposable utensils.

EXAMPLE 3

Further embodiments of the invention were prepared as described byExample 1. Nine were selected for having a tensile strength at about 20MPa or greater. These are set out by the data of Table 2. The granulesused as natural polymers for the Table 2 compositions were corn derivedstarch.

                  TABLE 2                                                         ______________________________________                                        Inventive                                                                              Wt. %    Wt. %     Other.sup.b                                                                          Tensile                                      Composition Starch Polymer.sup.a Wt. % Strength (MPa)                       ______________________________________                                        11       15       75        10     64.5                                         12 30 60 10 38.9                                                              13 45 45 10 20.6                                                              14 60 30 10 20.2                                                              15 45 45 10 25.2                                                              16 60 30 10 18.0                                                              7 45 45 10 18.3                                                               8 50 43 7 18.8                                                                9 55 38 7 18.6                                                              ______________________________________                                         .sup.a The hydroxyfunctional polyester was BIS CHD.                           .sup.b Compositions 11-14 included ESTAFLEX plasticizer                       (acetyltributylcitrate), compositions 15-16 included PARAPLEX plasticizer     (epoxidized soybean oil), compostions 7-9 included either PEG 3350 or PEG     20M plasticizer (polyethylene glycols).                                  

The data of Table 2 illustrates the uses of various optional components,such as different plasticizers, in compositions of the invention. Acomparison of inventive composition 3 from Table 1 with inventivecomposition 15 of Table 2 illustrates that the use of particularplasticizers can even moderately improve tensile strengths. This isanother example of the remarkable compatibility of the two essentialcomponents of the invention because plasticizer is normally used toimprove processing, but normally softens the composition.

Inventive compositions 16 and 7-9 of Table 2 and inventive compositions3 and 4 of Table 1 have tensile strength values in the range of about18-23 MPa. That is, these inventive compositions have better tensilestrength than the biodegradable compositions reported by Ramsey, supra,but by contrast to the Ramsey compositions the inventive compositionsincluded between about 45-60 wt. % starch granules (whereas the Ramseycompositions included only about 25 wt. % granular starch).

EXAMPLE 4

Yet more embodiments of the invention were prepared as described byExample 1, and four were selected for having a tensile strength aboveabout 20 MPa, the data for which are set out by Table 3.

                  TABLE 3                                                         ______________________________________                                        Inventive                                                                              Wt. %    Wt. %            Tensile                                      Composition Starch Polymer.sup.a Other Strength (MPa)                       ______________________________________                                        28       15       85        --     33.0                                         29 30 70 -- 46.7                                                              30 45 55 -- 41.8                                                              31 60 40 -- 25.6                                                            ______________________________________                                         .sup.a The hydroxyfunctional polyester was BIS Adipic.                   

The data of Table 3 illustrates inventive compositions with yet anotherhydroxy-functional polyester. While inventive composition 28 (with 15wt. % starch) has good tensile strength, it is considerably less thanthat found with inventive composition 1 where the hydroxy-functionalester was BIS CHD. However, with increased amounts of starch granules(in the range of 30 wt. % to 45 wt. % starch) the tensile strengthimproved.

FIG. 1 illustrates inventive composition 31. As illustrated, thediscontinuous starch granules are well adhered in the continuouspolyester phase. By contrast, non-inventive compositions of starch andwith various polyesters were found readily to fall apart and when viewedwith analogously magnified micrographs to have visible holes where thenon-adhered starch granules had fallen out.

EXAMPLE 5

Further embodiments prepared with a particularly preferredhydroxy-functional polyester, BIS DDCA, were prepared and selected forthe property of elongation.

                  TABLE 4                                                         ______________________________________                                        Inventive                                                                              Wt. %    Wt. %                                                         Composition Starch Polymer.sup.a Other Elongation (%)                       ______________________________________                                        23       15       85        --     679                                          24 30 70 -- 599                                                               25 45 55 -- 504                                                             ______________________________________                                         .sup.a The hydroxyfunctional polyester Was BIS DDCA.                     

Inventive compositions 23-25 gave outstanding elongation properties. Forcomparison, for example, the elongation to break (percent) for 100% highdensity polyethylene is 759. Thus, inventive compositions 23-25 comparequite favorably in elongation to 100% high density polyethylene, yetinclude up to 45 wt. % in starch granules.

EXAMPLE 6

The data of Table 5 illustrates use of yet another hydroxy-functionalpolyester for compositions of the invention, where the two inventivecompositions have excellent elongation properties.

                  TABLE 5                                                         ______________________________________                                        Inventive                                                                              Wt. %    Wt. %                                                         Composition Starch Polymer.sup.a Other Elongation (%)                       ______________________________________                                        19       15       85        --     426                                          20 30 70 -- 465                                                             ______________________________________                                         .sup.a The hydroxyfunctional polyester was HQ DDCA.                      

FIG. 2 illustrates inventive composition 19. One again sees theremarkable adherency of the granules in the hydroxy-functionalpolyester. This FIG. 2 micrograph was made after the elongation test hadbeen performed.

EXAMPLE 7

Unlike the preparations of Example 1, embodiments of the invention wereprepared where the starch granules were not pre-dried. Instead, starchgranules (containing about 10-11 wt. % water) were prepared in a manneranalogous to that reported in Example 1 but with no pre-drying step.From reviewing tests performed with these embodiments, we conclude thatthe pre-drying step, while preferred, does not appear necessary.Alternatively, if desired to remove some moisture from the granules,such could be done during an extrusion step rather than as a separate,pre-drying step.

EXAMPLE 8

The previously described examples 1-6 were compositions that were formedinto tensile bars. We turned to using compositions in another form.Thus, thin films having less than about 0.1 mm thickness were preparedwith a torque rheometer fitted with a one inch blown film die. The filmsobtained were conditioned at 23° C. and 50% relative humidity beforetesting. The data from Table 6 illustrate properties of two differentinventive compositions so formed into films.

                  TABLE 6                                                         ______________________________________                                        Inventive                                                                              Wt. %    Wt. %                                                         Composition Starch Polymer.sup.a Other.sup.b                                ______________________________________                                                                           Elongation (%)                               45 28 66 6 244                                                                    Tensile                                                                       Strength (MPa)                                                            44 30 70 --  17.4                                                           ______________________________________                                         .sup.a The hydroxyfunctional polyester was BIS Adipic.                        .sup.b Plasticizer was a modified polyethylene glycol.                   

EXAMPLE 9

Compositions were prepared with other starches or derivatized starches.Thus, diepoxide corn (a reaction product of bisphenol A diglycidyl ether(10%) and corn starch), hydroxyethyl corn, and corn flour were eachformulated with BIS Adipic polyesters in amounts of about 40%-50% flouror derivatized starch. However, the Table 3 compositions (using BISadipic) have to date been found to be preferred to all the flours andderivatized starches tested.

EXAMPLE 10

Another set of tensile bar formed compositions were prepared, butinstead of starch, flour or derivatized starch, the natural polymersused were either guar gum or cellulose. Both were in granule form withparticle sizes well below 100 μm. The method of preparation for thecompositions was the same as described in Example 1. Table 7 summarizesthe results.

                  TABLE 7                                                         ______________________________________                                        Inventive Composition                                                                           Tensile Strength (MPa)                                      ______________________________________                                        30 wt. % guar gum and                                                                           33                                                            70 wt. % Bis Adipic                                                           30 wt. % cellulose powder and 37                                              70 wt. % Bis Adipic                                                         ______________________________________                                    

EXAMPLE 11

Starch granules derived from potatoes were also formed into blends witha hydroxy-functional polyester having properties indicated by datagathered and set out by Table 8.

                  TABLE 8                                                         ______________________________________                                                      Tensile  Elongation                                               Strength (MPa) (%)                                                          ______________________________________                                        Control:                                                                        100% Polyester 21 705                                                         20% Potato Starch 12.7 370                                                    40% Potato Starch 6 190                                                       60% Potato Starch 7.45 14                                                   ______________________________________                                    

The polyester used in gathering the Table 8 data may be prepared asfollows.

A 13 L resin kettle, equipped with a mechanical stirrer and nitrogeninlet, is charged with hydroquinone diglycidyl ether (1312.5 g, 5.8 mol,113.06 g/equiv. epoxide), 1,10-decanedicarboxylic acid (1343.5 g, 5.83mol), and tetra-n-butylammonium bromide (94.2 g, 0.29 mol). Diglyme (3L) is added and the mixture heated to 110° C. for 5.5 hours under anatmosphere of nitrogen. Glacial acetic acid (250 mL) is added andheating at 110° C. is continued overnight. The solution is allowed tocool to about 50° C. and is poured into water in a large Waring blender(300 mL portions into 2 L water). The fibrous precipitate is collectedby suction filtration and suspended in fresh water for 3 days. Theproduct is collected by suction filtration and allowed to air-dryovernight. The product is dried in a vacuum oven at 100-115° C.overnight. The polymer has an inherent viscosity of 0.42 dL/g (DMF, 25°C., 0.5 G/DL), a Tg of 5° C., and a Tm of 75° C.

Dry blends of the above polyester and unmodified potato starch areprepared using the weight ratios indicated in Table 8. The blends arecompounded using a Haake mixer (60 cc bowl) at 120° C. for 6 minutes asindicated. Plaques (4"×4"×0.0625") are prepared by compression moldingthe material obtained from the Haake mixer. Specimens for mechanicalproperty testing are obtained from these plaques. Selected tensileproperties are listed in Table 8.

It is to be understood that while the invention has been described abovein conjunction with preferred specific embodiments, the description andexamples are intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims.

It is claimed:
 1. A formed article comprising:a continuous syntheticpolymer phase and granules of natural polymer dispersed therein, thesynthetic polymer phase including a hydroxy-flunctional polyester withrepeating units represented by Formula B: ##STR4## wherein each of R¹and R² is individually a divalent organic moiety which is predominatelyhydrocarbon, each R₃ is individually hydrogen or lower alkyl, y is afraction from 0 to 0.5, and x is a fraction from about 0.05 to about0.4, the natural polymer granules being starch, a starch ester, a starchether, a cross-linked starch, cellulose, or guar gum.
 2. The formedarticle as in claim 1 wherein the article has a tensile strength aboveabout 20 MPa or a tensile elongation above about 200 percent.
 3. Theformed article as in claim 1 wherein the natural polymer to polyester isin a weight ratio of up to about 6:1.
 4. The formed article as in claim1 wherein the granules have a particle size of less than about 100 μm.5. The formed article as in claim 1 wherein the granules have a particlesize of less than about 50 μm.
 6. The formed article as in claim 1wherein the granules have a water content of less than about 15 wt. %.7. The formed article as in claim 1 wherein R³ is individually hydrogenor methyl.
 8. The formed article as in claim 1 wherein the naturalpolymer granules have a particle size of less than about 50 μm and whenfrom a starch, a starch ester, or a starch ether are derived from agrain, a root, a legume, or mixtures thereof.
 9. The formed article asin claim 8 wherein the natural polymer constitutes between about 15% toabout 75% of the article by weight.
 10. The formed article as in claim 1further including one or more of a processing aid and a plasticizer anda filler.
 11. The formed article as in claim 1 wherein the naturalpolymer constitutes between about 40% and about 75% of the article byweight and the granules have a water content of less than about 11% byweight.
 12. The formed article as in claim 1 wherein the natural polymergranules include a corn starch and the corn starch constitutes betweenabout 15% to about 75% of the article by weight.
 13. The formed articleas in claim 1 wherein the natural polymer granules are substantiallyevenly dispersed throughout a matrix formed by the synthetic polymerphase.
 14. The formed article as in claim 1 wherein the polyester is BISCHD, whose repeating structure includes Formula C: ##STR5##
 15. Theformed article as in claim 1 wherein the synthetic polymer is BISadipic, whose repeating structure includes Formula D:
 16. The formedarticle as in claim 1 wherein the synthetic polymer is HG DDCA, whoserepeating structure includes Formula E:
 17. The formed article as inclaim 1 wherein the synthetic polymer is BIS DDCA, whose repeatingstructure includes Formula F:
 18. The formed article as in claim 1wherein each of R¹ and R² is individually a divalent aromatic moietyselected from the group consisting of m-phenylene, p-phenylene,isopropylidene, diphenylene, biphenylene, biphenylene oxide,methylenediphenylene, biphenylene sulfide, naphthylene,biphenylenecyanomethane, 3,3'-dialkyl-diphenytene-isopropylidene, and3,3',4,4'-tetraalkyldiphenylene-isopropylidene.
 19. The formed articleas in claim 1 wherein each of R¹ and R² is individually m-phenylene,p-phenylene, and isopropylidene diphenylene.
 20. The formed article asin claim 1 wherein each of R¹ and R² is individually a divalentaliphatic moiety selected from the group consisting of dialkyleneketone,dialklylenesulfone, dialkylenesulfoxide, dialkyleneoxide, anddialkylenesulfide.
 21. The formed article as in claim 1 wherein each ofR¹ and R² is individually a divalent aliphatic moiety selected from thegroup consisting of ethylene, propylene, and butylene.
 22. The formedarticle as in claim 1 wherein the forming has been by molding,extrusion, or casting.